Hi,
Have your timing adjusted using a timing light and not the epic laser vision of an ustad mechanic. Khyber's ignition timing at idle (800 rpms) is supposed to be set at 4 degrees. I don't know which city you're in, but if you're in Lahore you can have it done at Magic Motors which is in Model Town.
Regarding the actual problem that you're facing, check the following two things which are also related to ignition timing and could be the culprit to the problem.
1) There's a vacuum diaphragm hidden underneath the distributor which is supposed to be connected by a vacuum hose to a vacuum line behind the carburetor. When this isn't connected, the vacuum advance won't work and you'll face poor acceleration in the higher rev range.
2) For the same diaphragm, check whether it's able to hold vacuum or not. How you do that is attach a vacuum hose to the diaphragm and suck on the other end (You'll notice a rod like thing on the diaphragm that moves inside when you do this). Press the hose so that air won't be able to go inside it. The rod that's underneath the diaphragm is supposed to stay inside. If that comes out while you have the hose tightly pressed, then the diaphragm's gone bad and can't hold vacuum, so it will need to be replaced.
